In the cleaning of the fabrics in a paper or board machine, such as the wires and/or felts, jet pipes are used and extend across the entire width of the fabric in the transverse direction. These jet pipes include a series of nozzle holes through which high-pressure water jets are applied usually to the outer face of the fabrics to clean the fabric. The pressure of the washing water is sufficiently high to perform the desired cleaning operation, however, is normally less than about 35 bar.
Jet pipes are usually placed in connection with the return runs of the wires or felts in a paper machine. In the wire part of a paper or board machine, jet pipes are also used for cleaning of, e.g., the breast roll, the drive roll, and the wire-return rolls. With regard to wire-return rolls, jet pipes may also be used in connection with various doctor constructions. Further, jet pipes may be used, e.g., in connection with suction boxes and with devices for cleaning drying wires. Jet pipes are also used for internal cleaning of former rolls and suction rolls.
It is inevitable that on the inside faces and in the nozzle openings of the jet pipes, dirt or other impurities is deposited and must be cleaned from time to time, e.g., by means of brushes or equivalent cleansing means to prevent blockage of the jet pipe and to guarantee its reliable operation. The jet pipes are usually provided with a decontamination valve through which the water for cleaning/washing of the jet pipe is removed so that the removed contaminants do not enter into the object proper to be cleansed, i.e., the wire, felt or roll. For example, when paper is manufactured in three shifts, the jet pipes are cleaned, e.g., once during each shift.
In the prior art, a disc valve is used as the decontamination valve for a jet pipe. The disc valve closes the opening through which the used washing water is removed for the duration of the cleaning operation proper and use of the jet pipe. The valve is opened when the jet pipe itself is cleaned so that the cleaning/washing water is removed through the washing opening into a wash water duct. In a typical conventional arrangement, the disc valves are arranged in connection with the jet pipes so that they are closed against the pressure effective in the jet pipe. As a result, it is disadvantageous that it is difficult to close the valve and the valve may leak or, to be tight, at least require tightening to an extreme closing position.